"There are direct reasons why cannabis could actually help people get off of opioids," says one leading marijuana researcher.

Last year, a pharmaceutical company called Insys Therapeutics gave half a million dollars to the campaign to stop marijuana legalization in Arizona. The Phoenix-based company's flagship product is a prescription opioid spray made from fentanyl, an incredibly addictive and deadly drug estimated to be 50 times stronger than heroin. Cannabis, Insys knew, could disrupt the $24 billion market for painkillers and cost them business. After all, cannabis is now being used to treat many of the problems for which opioids are prescribed: back pain, arthritis, basically any kind of chronic discomfort. And there are some pretty convincing reasons why someone in pain might choose cannabis over opioids: Opioids are physically addictive, and can kill you. Cannabis has never killed anyone, and the withdrawal is mostly psychological.

Insys's cash injection seems to have worked – of the five states with adult-use cannabis legalization on the ballot in 2016, Arizona is the only place where it didn't pass. This, of course, is the root of the opioid crisis: pharmaceutical companies care more about profit than they do about human health. These companies are powerful, and they have been funding the anti-pot lobby for a long time. Still, in the face of opposition from entrenched interests and the federal government, a growing chorus of experts is calling for us to look into the possibility that legal cannabis could replace opioids in many circumstances, saving hundreds of thousands of lives over the course of the next decade.

The pain-relieving properties of cannabis are no longer hypothetical or anecdotal. At the beginning of the year, the National Academies of Science, Medicine and Engineering released a landmark report determining that there is conclusive evidence that cannabis is effective in treating chronic pain. What's even more promising is that early research indicates that the plant not only could play a role in treating pain, but additionally could be effective in treating addiction itself – meaning marijuana could actually be used as a so-called "exit drug" to help wean people off of pills or heroin.

"We're not just saying opioids make you feel good and so does cannabis, and now you're addicted to cannabis. There are direct reasons why this could actually help people get off of opioids," says Jeff Chen, director of UCLA's new Cannabis Research Initiative. "If there is a chronic pain component, the cannabis can address the chronic pain component. We also find opioid addicts have a lot of neurological inflammation, which we believe is driving the addictive cycle. We see in preliminary studies that cannabinoids can reduce neurological inflammation, so cannabis could be directly addressing the inflammation in the brain that's leading to opioid dependency."

The theory that cannabinoids could decrease cravings for opioids is further supported by a small 2015 study published in the journal Neurotherapeutics, which found that the non-psychoactive cannabinoid CBD was effective in reducing the desire for heroin among addicts, and remained effective for an entire week after being administered. Similar effects have long been observed in animal studies.

Cannabis, in fact, may be exactly the kind of opioid replacement that politicians and pharmaceutical executives claim to be searching for.

"I will be pushing the concept of non-addictive painkillers very, very hard," President Trump said in October, when declaring opioid abuse a national public health emergency. The CEO of Purdue Pharma, which makes OxyContin, recently referred to the possibility of a drug that helps with pain but isn't physically addictive as the "Holy Grail."

And yet the federal government maintains that the marijuana plant and its constituent compounds have no medical potential whatsoever. Perhaps that's because painkiller-producing pharmaceutical companies and their affiliated non-profits spent over $880 million nationwide on lobbying and political donations between 2006 and 2015. As Patrick Radden Keefe recently pointed out in the New Yorker, that's eight times the amount spent by the gun lobby in the same decade.

But already, many Americans seem to be replacing their pills with pot. A survey of pain patients in Michigan, published in 2016 in the journal of the American Pain Society, found medical cannabis use was associated with a 64 percent decrease in opioid use. A 2016 study published in the health policy journal Health Affairs found that states with medical marijuana saw a drop in Medicare prescriptions and spending for conditions that are commonly treated with cannabis, including chronic pain, glaucoma, seizures and sleep disorders. And a 21-month study of 66 chronic pain patients using prescription opioids in New Mexico found that those enrolled in the state's medical cannabis program were 17 times more likely to quit opioids than those who were not.

At the same time, opioid-related deaths and overdose treatment admissions appear to be declining by nearly 25 percent in states where patients have access to legal marijuana. That number comes primarily from a 2014 study in the Journal of the American Medical Association, and has been supported by additional data from the American Journal of Public Health, the American Academy of Nursing, and the Journal of Drug and Alcohol Dependence.

However, more research is sorely needed. Stanford professor and drug policy expert Keith Humphreys described the studies concerning cannabis legalization and the decrease in opioid-related deaths and hospital admissions as falling victim to a form of logical error known as ecological fallacy. "It's correlation, not causation," he told me, because you cannot use statistical information about entire populations to understand individual behavior.

And researchers are eager for more solid evidence. The Cannabis Research Initiative at UCLA is working on establishing one of the first studies that will directly administer cannabis to patients addicted to opioids, potentially providing a much more comprehensive understanding of how this all works. Chen, the initiative director, says he has scientists, clinics and a study design all lined up, but funding has been a struggle. "You're forced to go an extra ten miles with zero gas in the tank when it comes to cannabis research," he says. Between the lack of support from the federal government and pharmaceutical companies, Chen says he is "pretty much dependent on philanthropy."

Of course, if pharmaceutical companies thought they could make money off of marijuana, they would back legalization and help fund the UCLA study – but pot is just too difficult to patent and control. So the only kinds of cannabis that pharmaceutical companies are willing to look into are lab-created synthetic cannabinoids. These are easier to push through the FDA approval process and easier to patent, but are widely understood to be less effective than products made from the plant itself. Once again, helping patients is not as important as turning a profit.

Back in Arizona, Insys Therapeutics continues to pump out its addictive opioid spray, and possession of any amount of marijuana is still a felony. For allegedly stretching the truth and putting profits before patient safety, Insys is facing several lawsuits as well as a Congressional investigation. But the company is still open for business. A few weeks ago, Insys received DEA approval to start selling a new drug.